He's saving a vital part of America -- our music. His work, divided between performing familiar favorites and collecting music, is woven into a three-part documentary, PBS' "Michael Feinstein's American Songbook," beginning Wednesday, Oct. 6 (check local listings). It continues the next two Wednesdays.

Like most people with a guiding passion, Feinstein started young. By 5, he could hear a song and play it on the piano. At 54, rock is a more likely influence, but his tastes run toward Frank Sinatra.

"We are all responsible for preserving our heritage and music," Feinstein says. "It exists because it is passed on from one person to another. I hope people will have a greater awareness of this music and not throw away anything that could be valuable to a future generation."

Wearing jeans, a crisp white shirt and a navy blazer, Feinstein relaxes on the terrace of his Los Angeles mansion, explaining why sheet music and original recordings must be saved. He travels the country, meeting with the children of musicians, and leaves toting shopping bags of 78s and yellowing sheet music, the ephemera that make for a history of song.

All his life, Feinstein has been rifling through dusty stores, thumbing through LPs, then lugging home treasures to catalog. A center in Carmel, Ind., is under construction to house his collection.

Feinstein's affinity for these songs led him to the masters. As a young man, he worked for Ira Gershwin."Everything is a continuum," he says. "Elvis Costello and Billy Joel have a sense of history and have taken past music and created something."

Mementos from this continuum fill the exquisite mansion he shares with partner Terrence Flannery, who in the documentary discusses how he runs their day-to-day lives so Feinstein can concentrate on his work.

Going downstairs, there's a photo of a naked Liza Minnelli at the piano -- at age 3. He has one of the only two known posters for "The Jazz Singer," fittingly the movie that ushered out silent movies and heralded in talkies.

And there are the Gershwin files -- including an absolute gem of a photo of Gershwin in drag. Feinstein catalogs everything, and rooms are dedicated to sheet music and radio performances on tape, essentially a history of the American songbook.

This leads to the big question: Just what is the American songbook? Is any American song automatically in as a birthright?

"The songs I consider standards are primarily made up of accomplishments of writers most active from the '20s through the '50s," he says. "Time is the arbiter. Time determines what is classic, what lasts. Many songs that are hits today won't last. Time does clarify the essence of everything."

Inarguable, yet a bit of a mystical approach; Feinstein, though, is quite direct in embracing a song. Watching him onstage is to see the missionary of music at work: He loves spreading the word.

Sure, he sings old songs, but this is not an oldies concert. Instead, it's a celebration of music for people who appreciate the romance in a lyric.

He gives roughly 150 concerts a year and has a standing club act in Manhattan, Feinstein's at Lowes Regency. The documentary shows him there and at various venues.

In the first episode, "Putting on the Tailfins," Feinstein pays homage to Rosemary Clooney, whom he considers "the greatest female singer of the 20th century."

They did about 200 shows together, and Clooney referred to Feinstein as her "sixth kid."

Feinstein illustrates what's he been up against when he stands on Los Angeles' 405 freeway, on top of thousands of discarded scores -- used for landfill.

He explains how Sinatra's arrangements reflected the times, but Sinatra never had to try to make himself into something he wasn't.

"Sinatra owned the company," Feinstein says. "He called the shots."

"One of the things that people loved about the arrangements he sang in the '50s is that there was a macho sexuality about them, so in his own way Sinatra was bringing to an older audience the same thing that Elvis was bringing to a younger one," Feinstein says.

In the second episode, "Best Band in the Land," the film teaches how important music was during World War II as the government issued a monthly hit kit -- words and music to five American tunes and one Allied tune -- sent to 2 million soldiers.

Feinstein, who has performed for all U.S. presidents beginning with Ronald Reagan, put on a show at the Lincoln Memorial. He talks about Marian Anderson's concert there -- after the Daughters of the American Revolution revoked her invitation, and first lady Eleanor Roosevelt arranged to have the African-American singer perform.

By the third episode, "A New Step Every Day," he reminds us how small towns and cities across the country once had nightclubs, and people dressed up, went out and had fun. He works in the history and the sound, and by the end Feinstein has proven that the American Songbook 's wonderful, 's marvelous, and we should care for it.